This is the same/similar to this one, but I'm running the final version of 10.14.1. I can make the problem go away if I remove the following files from /Library/Preferences/SystemConfiguration/:
After a reboot, the captive login window works, but at some point, it stops working again and looks like:
I haven't tested much - I don't have regular access to many captive Wi-Fi networks.
I can work around the problem by dismissing the error, closing the window and using Safari to go to https://captive.apple.com, but I would like to solve the problem rather than work around it if possible.
Has anyone figured this out or can anyone point me in the right direction?